We applaud Matz et al. (1) for using field studies on Facebook to investigate the effectiveness of psychologically targeted messages, building on prior, largely laboratory-based research. That said, this comparison of Facebook ad campaigns does not randomly assign users to conditions, which threatens the internal validity of their findings and weakens their conclusions.

The paper uses Facebook’s standard ad platform to compare how different versions of ads perform. However, this process does not create a randomized experiment: users are not randomly assigned to different ads, and individuals may even receive multiple ad types (e.g., both extroverted and introverted ads). Furthermore, ad platforms like Facebook optimize campaign performance by showing ads to users whom the platform expects are more likely to fulfill the campaign’s objective (e.g., study 1, online …

Bacteria could help tackle the growing mountains of e-waste that plague the planet. Although researchers are a long way from optimizing the approach, some are already confident enough to pursue commercial ventures.

Holographic acoustic tweezers, in which ultrasonic waves produced by arrays of sound emitters are used to individually manipulate up to 25 millimeter-sized particles in three dimensions, could be used to create 3D displays consisting of levitating physical voxels.